1. Field of the Invention
The present invention relates generally to an injection molding apparatus and, in particular to a nozzle having a nozzle body with multiple nozzle body segments. More particularly, the present invention relates to an injection nozzle in which at least one of the nozzle body segments of the nozzle body is heaterless.
2. Background of the Invention
As is well known in the art, hot runner injection molding systems include a manifold for conveying pressurized melt from an inlet to one or more manifold outlets. A plurality of nozzles are typically coupled to the manifold outlets for conveying the melt to a plurality of mold cavities.
In some applications, such as molding of large automotive parts, it is necessary to use nozzles having different lengths, where the nozzles communicate with a single manifold. For example, when one is injecting a molten material into a mold cavity having an uneven surface facing the injection nozzles, then one of the nozzles has to be longer than the other to reach the mold cavity. In another example, when one is injecting a molten material simultaneously into separate mold cavities located in the same mold and having different heights or depths with respect to the tip portions of the nozzles, nozzles of different lengths are required. Such molds, often referred to as family molds, provide means to mold articles of different shapes at the same time using the same or different resins or metals.
To vary the length of the nozzles, one can use single body nozzles of different lengths, or one can use a combination of nozzles having a single nozzle body and nozzles having a nozzle body made of two nozzle body segments. In the later case, a single nozzle body segment can be connected with another nozzle body segment to vary the overall length of the nozzle body and thereby the overall length of the entire nozzle.
To maintain the temperature of the melt as it travels through the melt channel of the nozzle, one can use either a single heater or multiple heaters. In either case, in many instances, there is more heat lost at the ends of the nozzle adjacent the manifold and mold gate than in the mid-section. The mid-section of the nozzle does not contact any part of the manifold or mold plate and, therefore, does not lose heat as quickly as at the ends. In long nozzles that are heated by a single heater, the mid-section retains heat more efficiently than the end portions. As a result, the temperature of the nozzle mid-section is often difficult to regulate if a single heater is used along the nozzle or melt channel. Thus, the temperature of the melt along the mid-section of the nozzle is higher than at the ends. This uneven heat profile is difficult to correct or control.
The uneven heat profile along the melt channel is undesirable because any variation in the temperature of the melt as it flows through the injection molding apparatus can adversely affect the quality of the molded products. The uneven heat distribution along the nozzle and melt channel is often exaggerated when longer nozzles, including nozzles having a nozzle body comprised of two nozzle body segments, are used.
In order to compensate for the uneven heat distribution along the length of the nozzle, a conventional nozzle heater is used. The nozzle heater includes a heating element that is wound around the nozzle body. The pitch of the heating element is typically smaller near the nozzle head and nozzle tip and larger along the nozzle mid-section in order to compensate for the uneven heat loss experienced by the nozzle. A disadvantage of this arrangement is there is often a temperature spike at the mid-section of the nozzle because these conventional heater still applies heat along the entire length of the nozzle and the heat loss from the mid-section is negligible compared to the heat loss from the ends of the nozzle.
There is a need to provide a way to mold parts having uneven surfaces or to simultaneously mold various parts having different shapes in a single mold by using injection nozzles of variable length. There is also a need to better control and correct the heat profile along variable length nozzles. There is also a need to manufacture injection nozzles in various lengths in a faster and more efficient manner, while still being able to easily customize the length of the nozzle, or to manufacture and assemble the injection nozzles in different remote locations.